Monolithic tubes having tunnels along the length thereof are useful for a variety of purposes. Thus, for example, thus, for example, monolithic tubes made of an adsorbent material and having parallel tunnels along the length thereof for the passage of gas may be used for the separation or purification of gases from gas mixtures. Similar structures made from other materials, such as cement, may be used for withdrawing and storing heat from fluids passing through the tunnels. Furthermore, in the fabrication of elongated monolithic structures, such as rods, the incorporation of a desired amount of void space in the form of parallel tunnels may be used to achieve a balance between strength and weight may be achieve a balance between strength and weight.
The use of adsorption materials for the separation or purification of gases from gas mixtures is known. Thus, for example, gases to be purified or gas mixtures to be separated with the aid of an adsorbent may be passed through vessel filled with particles of the adsorbent (particle bed). When the gas contacts the adsorbent, some is adsorbed. The selectivity of the adsorbent will allow some gases to pass through readily but will preferentially adsorb other gases. For example, silica gel will adsorb water vapor in preference to the other components of air and the air will therefore be dried. Some adsorbents will adsorb nitrogen much more readily than oxygen and, therefore, the gas emerging from the adsorbent vessel will have a higher concentration of oxygen than the air entering the vessel. When the adsorbent becomes filled or saturated with the gases that are preferentially adsorbed, the gas will pass through without changing its concentration. The adsorbent must then be desorbed to remove the adsorbed gases. The adsorbent may then be used again.
There are difficulties associated with the use of particle bed-type adsorbent vessels. For example, gas velocity must be very carefully controlled to avoid lifting of the particles or channeling of the gas through the particle bed. Furthermore, the bed must be maintained in a position for vertical flow of the gas. If the flow of gas is horizontal, the particles will tend to settle and the gas will be able to flow above the bed without particle contact. Moreover, the adsorbent particle distribution (by size) is important to the quality and capacity of the system. If, on settling, the smaller particles migrate and settle near the circumference of the vessel, it will cause a higher gas flow rate to occur at the vessel center where adsorption will take place preferentially and as that region becomes saturated, gases will pass through without adsorption and the particles near the circumference will be unused or underused.
The problems associated with the particle bed-type adsorbent vessels may be overcome with the use of monolithic adsorption tubes that may be formed by extrusion techniques and, in particular, with the use of the method and novel extrusion die of the present invention.
Various techniques and extrusion dies are disclosed in the literature for the extrusion of ceramic batches, plastics, cement, clay, adsorbents and similar materials which have the property of being able to flow or plastically deform during extrusion while being able to become sufficiently rigid thereafter so as to maintain structural integrity. Such techniques and dies have been used for the manufacture of various monolithic or honeycomb type of structures having a plurality of openings or passages extending therethrough.
U.S. Pat. No. 1,849,431 discloses the manufacture of clay conduits using a die assembly wherein a cross-head positions a plurality of spaced bells are mounted on longitudinal stems, which secured to bridges spanning the die side wall. The bells are of non-circular shape corresponding to the shape of the various passages to be formed in the conduit.
U.S. Pat. No. 3,406,435 discloses apparatus for manufacturing ceramic elements having a honeycomb structure wherein a plurality of elongated thin-walled sleeve members having extensions with closed end portions are connected to an extruder cylinder. The material to be extruded is forced through the elongated sleeve members and outwardly through orifices formed in side walls of the extensions attached thereto. The sleeve extensions are spaced from each other to provide channels in which the material from the orifices becomes reshaped into a honeycomb structure.
U.S. Pat. No. 3,905,743 discloses an extrusion die for forming thin-walled honeycomb structures. The extrusion die is of unitary construction having a plurality of interconnected discharge slots provided with uniform openings in the outlet face of the die.
Although a variety of extrusion dies and methods of use are set forth in the prior art, it will be apparent to those skilled in the art that need exists for an extrusion die apparatus that is less expensive and conveniently adaptable for the extrusion of monolithic tubes, such as, monolithic adsorption tubes and the like having variable numbers and sizes of longitudinal openings for the passage of fluids.